The present invention relates to a system for controlling the ground speed of a maneuverable off-road vehicle and, more specifically, relates to an interconnected system for controlling the ground speed of lawn and garden tractors and front mount mowers having hydrostatic transmissions, a specific type of variable speed transmission.
It is known to provide off-road vehicles, specifically small tractors and front mount mowers with systems for controlling their ground speed. Such vehicles usually are equipped with conventional systems for: selectively operating the vehicle in either the forward or reverse direction (engine, transmission, drive train); selectively stopping the ground motion of the vehicles (brakes); and selectively utilizing the brakes to assist with vehicle's maneuverability (left and right turn brakes). It is also known to provide such vehicles with a cruise control system for selectively maintaining or disengaging the position of a swash plate or control shaft.
Additionally, it is known to be very desirable to initially precisely locate and establish the hydrostatic or variable speed transmission's neutral position such that when in the neutral position, there is no ground movement or creep in either the forward or the reverse direction. Further, after initially establishing a precise neutral position, it is also desirable to either eliminate or at least reduce subsequent adjustments in order to maintain this initial precise location.
With respect to maintaining a constant swash plate or control shaft position, it has long been desirable to develop not only a reliable cruise control system but one which incorporate a plurality of rapid disengagement means which, when necessary, allows an operator to rapidly disengage the cruise control system in order to regain normal control of the vehicle.
Another previously unrealized goal of designers in the art relates to means for preventing the vehicle from being driven with the parking brake partially engaged or for preventing the operator from accidentally depressing a forward or reverse control pedal such as when mounting the vehicle thereby causing the vehicle to accelerate in either the forward or reverse direction. It is well known to provide a throttle and a gear selector attached to the engine, transmission and drive train for selectively operating the vehicle in either the forward or reverse directions. It is also well known to provide a system for selectively stopping the vehicle when operating in the forward and reverse directions. It is further well known to provide foot brakes to assist with vehicle maneuverability.
With respect to methods and apparatus for precisely locating the neutral position of a hydrostatic transmission, U.S. Pat. No. 3,488,955 commonly owned with the present application, illustrates one attempt to solve this problem. While the mechanical linkage disclosed did improve the initial location and subsequent return of the swash plate to the hydro neutral position, wear in the surfaces of the cam roller and the groove, could, over time, cause creep.
With regard to cruise control systems for off-road vehicles having hydrostatic transmissions, previously known systems have not incorporated at least three methods for positively effectuating cruise control disengagement.
A typical cruise control system utilizes a friction device to maintain the position of the swash plate. These friction devices can present problems, since the tendency of hydrostatic transmissions under load, such as going up a hill, is to seek the neutral position, the friction contact can be broken resulting in the vehicle slowing down. This naturally requires that the operator place the vehicle back in the cruise mode by reengaging the friction device. Obviously any friction device will, over time, suffer from wear. Thus, the cruise controls containing friction devices could require frequent replacement.
Accordingly, there is a need for an improved system and method for controlling the ground speed of a maneuverable offroad vehicle having a variable speed transmission, specifically a hydrostatic transmission which provides an operator with precise control of the vehicle. Such a system should have a precisely located neutral position; a foot controlled system for operating the vehicle in both the forward and reverse directions; a system for stopping the vehicle or brake system which includes: a left and right turn brake system for enhancing the vehicles maneuverability; a service brake system for emergency, rapid stopping and a park brake system; a system for selectively maintaining a constant control shaft or swash plate position when the vehicle is being operated in the forward direction only or "cruise control" system; at least three positive, separate means for disengaging the cruise control and a system for interconnecting the cruise control system, the foot controlled operating system and the brake system.